export function  dataURLtoFile(dataurl,filename) { //将base64转换为文件
    var arr = dataurl.split(","),
    mime = arr[0].match(/:(.*?);/)[0],
    bstr = atob(arr[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new File([u8arr], filename, { type: mime });

}